1. Field of the Invention
The invention relates to a vibration generator comprising a piston guided in a linear manner, which is connected with a crankshaft by a connecting rod. The piston is connected with the connecting rod by a piston pin bearing, and the crankshaft is connected with the connecting rod by a crank journal.
2. The Prior Art
In construction, vibration generators such as vibrators, shakers, or vibration bears, are used to introduce profiles into the ground, or to draw them from the ground, or also to compact ground material. The ground is excited by the vibration, and thereby achieves a “pseudo-fluid” state. The goods to be driven in can then be pressed into the construction ground by a static top load. The vibration is characterized by a linear movement and is generated by rotating imbalances that run in opposite directions, in pairs, within a vibrator drive. The rotating imbalance masses bring about a force effect that describes a sine curve, over time. Such a drive acts alternately in the forward drive direction and counter to it, with time offset. The forward drive direction is determined, in the final analysis, by means of static forces, such as the inherent weight and static top loads. Without the superimposition of static forces on the vibration, the material being driven would not move forward, but rather simply vibrate back and forth.
To overcome the aforementioned disadvantages, German Patent Application DE 196 39 786 A1 proposes to dispose an imbalance mass mounted so as to rotate, in the manner of a crank gear mechanism, offset by a defined eccentricity perpendicular to its drive shaft. Because of the eccentricity, the imbalance mass performs a rotation at non-uniform angular velocity while the angular velocity of the drive remains constant, so that the amount of the centrifugal force changes as a function of its direction. The rotating slider crank mechanism described in DE 196 39 787 A1 shows a comparatively simpler structure. Such rotating slider crank mechanisms have a simple structure and furthermore demonstrate little noise development.
However, it is a disadvantage of the previously known systems that the geometric conditions prove to be very problematic. The directed work method of the rotating slider crank mechanism is based on the fact that the connecting rod is structured to be small relative to the crank radius. In contrast, the crank radius itself has to be minimized, however, in order to limit the idle power, which increases as the square of the piston path. Furthermore, because of the geometry, the connecting rod must be structured to be longer than the sum of the radii of the crank journal and piston pin bearings. However, these bearings must be structured to have a size in accordance with the forces that are applied. To fulfill the aforementioned contradictory requirements, the connecting rod length and the crank radius must be selected to be appropriately great; the resulting great idle power can be countered by a large mass inertia moment of the crankshaft provided by the design. It is a disadvantage of this arrangement that the vibration generator is dimensioned to be large and heavy, resulting in unnecessarily great speeds and friction powers.